Display device and fabrication method thereof

ABSTRACT

A display device includes a substrate that includes a display region and a non-display region that surrounds the display region, a plurality of pixels disposed on the display region of the substrate, a plurality of dam members disposed on the non-display region of the substrate that surround the display region, a first encapsulation layer disposed on the substrate that covers the pixels and the dam members, and a second encapsulation layer disposed on the first encapsulation layer and in a region between the display region and a dam member of the plurality of the dam members that is adjacent to the display region. A surface roughness of a top surface of the second encapsulation layer is greater than a surface roughness of a top surface of the first encapsulation layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non provisional patent application claims priority under 35U.S.C. § 119 from, and the benefit of, Korean Patent Application No.102017-0177457, filed on Dec. 21, 2017 in the Korean IntellectualProperty Office, the contents of which are herein incorporated byreference in their entirety.

BACKGROUND

Embodiments of the present disclosure are directed to a display deviceand a method of fabricating the same, and in particular, to a displaydevice that includes a thin encapsulation layer and a method offabricating the same.

An organic light emitting display device is a display device in which anorganic material is used as a light emitting device. In an organic lightemitting display device, recombinations of electrons and holes are usedto generate light, and such light is used to display an image. Anorganic light emitting display device does not require an additionallight source, unlike a liquid crystal display device, and have excellentbrightness and a wide viewing angle. In addition, an organic lightomitting display device has a fast response speed and a low powerconsumption.

To fabricate a organic light emitting display device, a plurality ofpixels that include light-emitting devices are formed on a substrate,and then, a thin encapsulation layer is provided on the substrate tocover the pixels. The thin encapsulation layer includes an inorganicinsulating layer and an organic insulating layer. The organic insulatinglayer is formed by forming a fluidic organic material on the substrateand then curing the organic material. When providing the organicmaterial on the substrate, the fluidic organic material may flow towardan unintended region or may overflow the substrate.

SUMMARY

Some embodiments of the inventive concept provide an organic materialfor a thin encapsulation layer in a desired region and can prevent theorganic material from overflowing the substrate, a method of fabricatinga display device, and a display device fabricated thereby.

According to some embodiments of the inventive concept, a display deviceincludes a substrate that includes a display region and a non-displayregion that surrounds the display region, a plurality of pixels disposedon the display region of the substrate, a plurality of dam membersdisposed on the non-display region of the substrate that surround thedisplay region, a first encapsulation layer disposed on the substratethat covers the pixels and the dam members, and a second encapsulationlayer disposed on the first encapsulation layer and in a region betweenthe display region and a dam member of the plurality of the dam membersthat is adjacent to the display region. A surface roughness of a topsurface of the second encapsulation layer may be greater than a surfaceroughness of a top surface of the first encapsulation layer.

In some embodiments, a thickness of the second encapsulation layer maybe less than a thickness of the first encapsulation layer.

In some embodiments, the surface roughness of the second encapsulationlayer may range from 8.4 nm to 35 nm, and the surface roughness of thefirst encapsulation layer may range from 0.9 nm to 2 nm.

According to some embodiments of the inventive concept, a display deviceincludes a substrate that includes a display region and a non-displayregion that surrounds the display region; a plurality of pixels disposedon the display region of the substrate; a plurality of dam membersdisposed on the non-display region of the substrate that surround thedisplay region; a first encapsulation layer disposed on the substratethat covers the plurality of pixels and the plurality of dam members;and a second encapsulation layer disposed on the first encapsulationlayer and in a region between the display region and a dam member of theplurality of dam members that is adjacent to the display region. Thefirst encapsulation layer comprises silicon oxynitride, the secondencapsulation layer comprises silicon oxynitride or silicon oxide, andthe first and second inorganic materials differ from each other in termsof composition ratios of silicon, oxygen, and nitrogen.

According to some embodiments of the inventive concept, a method offabricating a display device includes preparing a substrate thatincludes a display region and a non-display region that surrounds thedisplay region, forming a plurality of pixels on the display region ofthe substrate, forming a plurality of dam members on the non-displayregion of the substrate to surround the display region, forming a firstencapsulation layer on the substrate that covers the pixels and the dammembers, and forming a second encapsulation layer on the firstencapsulation layer and in a region between the display region and a dammember of the plurality of dam members that is adjacent to the displayregion. The second encapsulation layer has a top surface whose surfaceroughness is greater than a surface roughness of a top surface of thefirst encapsulation layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a display device according to some embodimentsof the inventive concept.

FIG. 2 is an equivalent circuit diagram of a pixel of FIG. 1.

FIG. 3 is a sectional view of a pixel of FIG. 2.

FIG. 4 is a sectional view taken along line I-I′ of FIG. 1.

FIG. 5 is an enlarged sectional view of an end portion of a secondencapsulation layer shown in FIG. 4.

FIGS. 6 to 11 are sectional views that illustrate a method offabricating a display device according to some embodiments of theinventive concept.

FIGS. 12 and 13 are sectional views that illustrate a method offabricating a display device according to other embodiments of theinventive concept.

It should be noted that these figures are intended to illustrate thegeneral characteristics of methods, structure and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. However, the relative thicknesses and positioning ofmolecules, layers, regions and/or structural elements may be reduced orexaggerated for clarity. The use of similar or identical referencenumbers in the various drawings may indicate the presence of a similaror identical element or feature.

DETAILED DESCRIPTION

Exemplary embodiments of the inventive concept will now be describedmore fully with reference to the accompanying drawings, in whichexemplary embodiments are shown. Exemplary embodiments of the inventiveconcept may, however, be embodied in many different forms and should notbe construed as being limited to the embodiments set forth herein. Inthe drawings, the thicknesses of layers and regions may be exaggeratedfor clarity. Like reference numerals in the drawings may denote likeelements, and thus their description will be omitted.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent.

FIG. 1 is a plan view of a display device according to some embodimentsof the inventive concept.

Referring to FIG. 1, according to embodiments, a display device 100includes a display panel 110, a scan driver 120, a data driver 130, anemission driver 140, and a plurality of dam members DM1 and DM2. Thedisplay panel 110 may be an organic light emitting display panel, butembodiments of the inventive concept are not limited thereto. Forexample, other types of display panels, such as a liquid crystal displaypanel, an electrowetting display panel, or an electrophoretic displaypanel, can be used as the display panel 110.

According to an embodiment, the display panel 110 is a flexible displaypanel. The display panel 110 has a rectangular shape whose short sidesare parallel to a first direction DR1 and whose long sides are parallelto a second direction DR2 that crosses the first direction DR1. Thedisplay panel 110 has a flat surface which is parallel to a planedefined by the first direction DR1 and the second direction DR2, and theflat surface of the display panel 110 includes a display region DA and anon-display region NDA surrounding the display region DA. The displayregion DA is used to display an image, and the non-display region NDA isnot used to display an image.

According to an embodiment, the display panel 110 includes a pluralityof pixels PX, a plurality of scan lines SL1-SLm, a plurality of datalines DL1-DLn, and a plurality of light-emitting lines EL1-Elm, where mand n are natural numbers. For convenience in illustration, only onepixel PX is illustrated in FIG. 1, but actually, the plurality of pixelsPX are provided in the display panel 110. The pixels PX are arranged ina matrix shape in the display region DA and are connected to the scanlines SL1-SLm, the data lines DL1-DLn, and the light-emitting linesEL1-ELm.

According to an embodiment, the scan driver 120, the data driver 130,and the emission driver 140 are provided in the non-display region NDA.The scan driver 120 is disposed in a region of the non-display regionNDA along one of long sides of the display panel 110. The emissiondriver 140 is disposed in another region of the non-display region NDAalong an opposite one of the long sides of the display panel 110. Thedata driver 130 is an integrated circuit chip and is disposed in otherregion of the non-display region NDA along one of short sides of thedisplay panel 110.

According to an embodiment, the scan lines SL1-SLm extend in the firstdirection DR1 from connections with the scan driver 120 and receive scansignals from the scan driver 120. The data lines DL1-DLn extend in thesecond direction DR2 from connections with the data driver 130 andreceive data voltages from the data driver 130. The light-emitting linesEL1-Elm extend in the first direction DR1 from connections with theemission driver 140 and receive light emitting signals from the emissiondriver 140.

According to an embodiment, the scan driver 120 generates a plurality ofscan signals that are transmitted to the pixels PX through the scanlines SL1-SLm. The scan signals are sequentially transmitted to thepixels PX. The data driver 130 generates a plurality of data voltagesthat are transmitted to the pixels PX through the data lines DL1-DLn.The emission driver 140 generates a plurality of light emitting signalsthat are transmitted to the pixels PX through the light-emitting linesEL1-ELm.

According to an embodiment, the display device 100 includes a timingcontroller that controls operations of the scan driver 120, the datadriver 130, and the emission driver 140. The timing controller generatesscan control signals, data control signals, and light-emitting controlsignals in response to control signals received from the outside. Inaddition, the timing controller receives image signals from the outside,converts the image signals into a data format compatible with thespecifications of the data driver 130, and transmits the converted imagedata to the data driver 130.

According to an embodiment, the scan driver 120 generates scan signalsin response to the scan control signal, and the emission driver 140generates light emitting signals in response to the light-emittingcontrol signal. The data driver 130 receives the converted image dataand then generates data voltages corresponding to the converted imagedata, in response to the data control signal.

According to an embodiment, the pixels PX receive data voltages inresponse to the scan signals. The pixels PX emit light having abrightness level corresponding to the data voltage in response to thelight emitting signals to display an image. A light-emitting duration ofthe pixel PX is controlled by the light emitting signals.

According to an embodiment, the dam members DM1 and DM2 are disposed inthe non-display region NDA and surround the display region DA. The dammembers DM1 and DM2 extend along an edge region of the display panel 110and surround the scan driver 120, the data driver 130, and the emissiondriver 140. Two dam members DM1 and DM2 are illustrated as an example ofthe inventive concept, but embodiments are not limited thereto, and thenumber of the dam members DM1 and DM2 is not limited to two.

According to an embodiment, the dam members DM1 and DM2 include a firstdam member DM1 which surrounds the display region DA, and a second dammember DM2 which surrounds the first dam member DM1. The first andsecond dam members DM1 and DM2 will be described in more detail below.

FIG. 2 is an equivalent circuit diagram of a pixel of FIG. 1.

Although only one pixel PX is illustrated in FIG. 2, the pixels PX ofthe display panel 110 have the same structure as the pixel PX shown inFIG. 2.

Referring to FIG. 2, according to an embodiment, the pixel PX isconnected to a corresponding one (e.g., SLi) of the scan lines SL1-SLm,a corresponding one (e.g., DLj) of the data lines DL1-DLn, and acorresponding one (e.g., ELi) of the light-emitting lines EL1-Elm, wherei is a natural number less than or equal to m and j is a natural numberless than or equal to n. The pixel PX includes a light-emitting deviceOLED, a driving transistor T1, a capacitor Cst, a switching transistorT2, and a light-emitting control transistor T3. The light-emittingdevice OLED is an organic light emitting diode.

According to an embodiment, a first voltage ELVDD is transmitted to asource terminal of the driving transistor T1, and a drain terminal ofthe driving transistor T1 is connected to a source terminal of thelight-emitting control transistor T3. A gate terminal of the drivingtransistor T1 is connected to a drain terminal of the switchingtransistor T2.

According to an embodiment, a gate terminal of the switching transistorT2 is connected to the scan line SLi, and a source terminal of theswitching transistor T2 is connected to the data line DLj. A firstelectrode of the capacitor Cst is connected to the source terminal ofthe driving transistor T1, and a second electrode of the capacitor Cstis connected to the gate terminal of the driving transistor T1.

According to an embodiment, a gate terminal of the light-emittingcontrol transistor T3 is connected to the light-emitting line ELi, and adrain terminal of the light-emitting control transistor T3 is connectedto an anode electrode of the light-emitting device OLED. A cathodeelectrode of the light-emitting device OLED receives a second voltageELVSS. The second voltage ELVSS has a voltage level lower than that ofthe first voltage ELVDD.

According to an embodiment, the switching transistor T2 is turned on inresponse to a scan signal SCAN received through the scan line SLi. Whenthe switching transistor T2 is turned on, a data voltage VD receivedthrough the data line DLj is transmitted to the gate terminal of thedriving transistor T1. The capacitor Cst is charged to the data voltageVD transmitted to the gate terminal of the driving transistor T1 and ismaintained at the data voltage VD, even after the switching transistorT2 is turned off.

According to an embodiment, when a light-emitting signal EM is receivedby the gate terminal of the light-emitting control transistor T3 throughthe light-emitting line Eli, the light-emitting control transistor T3 isturned on in response to the light-emitting signal EM. In this case, thelight-emitting control transistor T3 is used to transmit a current Ioledfrom the driving transistor T1 to the organic light emitting diode OLED.The pixel PX emits light during a period in which it receives thelight-emitting signal EM. An intensity of light emitted from thelight-emitting device OLED can change depending on the magnitude of thecurrent Ioled.

According to an embodiment, the transistors T1-T3 of the pixel PX may bePMOS transistors, but embodiments of the inventive concept are notlimited thereto. For example, the transistors T1-T3 of the pixel PX maybe NMOS transistors.

FIG. 3 is a sectional view of a pixel of FIG. 2.

Referring to FIG. 3, according to an embodiment, the pixel PX includesthe light-emitting device OLED and a transistor TR connected to thelight-emitting device OLED. The transistor TR is the light-emittingcontrol transistor T3. The transistor TR and the light-emitting deviceOLED are disposed on a substrate SUB, and the substrate SUB is atransparent flexible substrate formed of a flexible plastic material.For example, the substrate SUB may be formed of or include polyimide(PI).

According to an embodiment, a buffer layer BFL is disposed on thesubstrate SUB and is formed of or includes an inorganic material. Asemiconductor layer SM of the transistor TR is provided on the bufferlayer BFL. The semiconductor layer SM may be formed of or include aninorganic semiconductor material, such as amorphous silicon or polysilicon, or an organic semiconductor material. In addition, thesemiconductor layer SM may be formed of or include an oxidesemiconductor material. In addition, the semiconductor layer SM includesa source region, a drain region, and a channel region between the sourceregion and the drain region.

According to an embodiment, a first insulating layer INS1 is disposed onthe buffer layer BFL that covers the semiconductor layer SM. The firstinsulating layer INS1 is formed of or includes an inorganic material. Agate electrode GE of the transistor TR is disposed on the firstinsulating layer INS1 that overlaps the semiconductor layer SM. The gateelectrode GE overlaps the channel region of the semiconductor layer SM.

According to an embodiment, a second insulating layer INS2 is disposedon the first insulating layer INS1 that covers the gate electrode GE.The second insulating layer INS2 is an interlayer insulating layer. Thesecond insulating layer INS2 is formed of or includes an organicmaterial and/or an inorganic material.

According to an embodiment, a source electrode SE and a drain electrodeDE of the transistor TR are disposed on the second insulating layer INS2and are spaced apart from each other. The source electrode SE isconnected to a source region of the semiconductor layer SM through afirst contact hole CH1 that penetrates the first insulating layer INS1and the second insulating layer INS2. The drain electrode DE isconnected to a drain region of the semiconductor layer SM through asecond contact hole CH2 that penetrates the first insulating layer INS1and the second insulating layer INS2.

According to an embodiment, a third insulating layer INS3 is disposed onthe second insulating layer INS2 that covers the source electrode SE andthe drain electrode DE of the transistor TR. The third insulating layerINS3 is a planarization layer that provides a flat top surface and isformed of or includes an organic material.

According to an embodiment, a first electrode E1 of the light-emittingdevice OLED is disposed on the third insulating layer INS3. The firstelectrode E1 is connected to the drain electrode DE of the transistor TRthrough a third contact hole CH3 that penetrates the third insulatinglayer INS3. The first electrode E1 is a pixel electrode or an anodeelectrode. The first electrode E1 includes a transparent electrode orreflective electrode.

According to an embodiment, a pixel definition layer PDL is disposed onthe first electrode E1 and the third insulating layer INS3 and exposes aportion of the first electrode E1. A pixel opening PX_OP in the pixeldefinition layer PDL exposes a specific portion of the first electrodeE1, and a region having the pixel opening PX_OP is defined as a pixelregion PA. A region around the pixel region PA is defined as a non-pixelregion NPA.

According to an embodiment, an organic light emitting layer OEL isdisposed in the pixel opening PX_OP and on the first electrode E1. Theorganic light emitting layer OEL is formed of or includes an organicmaterial that can generate one of red, green, or blue light. However,embodiments of the inventive concept are not limited thereto, and theorganic light emitting layer OEL may be formed of organic materials thatcan combine red, green, and blue lights to generate a white light.

According to an embodiment, the organic light emitting layer OEL isformed of or includes a low molecular organic material or a polymerorganic material. In addition, the organic light emitting layer OEL hasa multi-layered structure that includes a hole injection layer (HIL), ahole transporting layer (HTL), a light emitting layer (EML), an electrontransporting layer (ETL), and an electron injection layer (EIL). Thehole injection layer is disposed on the first electrode E1, and the holetransporting layer, the light emitting layer, the electron transportinglayer, and the electron injection layer are sequentially stacked on thehole injection layer.

According to an embodiment, a second electrode E2 is disposed on thepixel definition layer PDL and the organic light emitting layer OEL. Thesecond electrode E2 is a common electrode or a cathode electrode. Thesecond electrode E2 includes a transparent electrode or a reflectiveelectrode.

According to an embodiment, when the display panel 110 is a top-emissiontype organic light emitting display panel, the first electrode E1 andthe second electrode E2 serve as a reflective electrode and atransparent electrode, respectively. According to an embodiment, whenthe display panel 110 is a bottom-emission type organic light emittingdisplay panel, the first electrode E1 and the second electrode E2 serveas a transparent electrode and a reflective electrode, respectively.

According to an embodiment, the light-emitting device OLED is formed inthe pixel region PA and includes the first electrode E1, the organiclight emitting layer OEL, and the second electrode E2 in the pixelregion PA. The first electrode E1 is a hole injection electrode or apositive electrode, and the second electrode E2 is an electron injectionelectrode or a negative electrode.

According to an embodiment, a thin encapsulation layer TFE is disposedon the substrate SUB that covers the pixel PX. The thin encapsulationlayer TFE includes a first encapsulation layer EN1 on the substrate SUBthat covers the light-emitting device OLED, a second encapsulation layerEN2 on the first encapsulation layer EN1, a third encapsulation layerEN3 on the second encapsulation layer EN2, and a fourth encapsulationlayer EN4 on the third encapsulation layer EN3. Each of the first,second, and fourth encapsulation layers EN1, EN2, and EN4 is formed ofor includes an inorganic insulating material, and the thirdencapsulation layer EN3 is formed of or includes an organic insulatingmaterial.

According to an embodiment, to allow the organic light emitting layerOEL of the light-emitting device OLED to emit light, the first voltageELVDD is transmitted to the first electrode E1 through the transistorTR, and the second voltage ELVSS, whose sign is opposite to the firstvoltage ELVDD, is transmitted to the second electrode E2. Holes andelectrons injected into the organic light emitting layer OEL combine toform excitons, and light is emitted from the light-emitting device OLEDwhen the excitons decay back to a ground state. The light-emittingdevice OLED emits red, green, or blue light to display an image.

FIG. 4 is a sectional view taken along line I-I′ of FIG. 1. FIG. 5 is anenlarged sectional view of an end portion of a second encapsulationlayer shown in FIG. 4.

Referring to FIGS. 4 and 5, according to an embodiment, the substrateSUB includes a display region DA and a non-display region NDA, and thedisplay region DA of the substrate SUB includes the pixel region PA andthe non-pixel region NPA. The pixel PX is disposed on the display regionDA of the substrate SUB. The first and second dam members DM1 and DM2are disposed on the non-display region NDA of the substrate SUB andenclose the display region DA.

According to an embodiment, the scan driver 120 includes a plurality oftransistors, and the transistors of the scan driver 120 are disposed onthe substrate SUB. For convenience of illustration, only one transistorTS of the scan driver 120 is illustrated in FIG. 4. Furthermore, in asectional view of FIG. 4, a region with the scan driver 120 is shown asbeing smaller than an actual region.

According to an embodiment, the buffer layer BFL and the firstinsulating layer INS1 are disposed on the display region DA and thenon-display region NDA of the substrate SUB. The second insulating layerINS2 is disposed on the display region DA of the substrate SUB andextends to cover a region of the non-display region NDA adjacent to thefirst dam member DM1.

According to an embodiment, the third insulating layer INS3 is disposedon the display region DA of the substrate SUB and extends into thenon-display region NDA and includes a portion adjacent to the first dammember DM1 and on the second insulating layer INS2. The third insulatinglayer INS3 covers the transistors TR and TS. The second electrode E2 ofthe light-emitting device OLED extends into the non-display region NDAand is disposed on the third insulating layer INS3 in the non-displayregion NDA.

According to an embodiment, a height of a top surface of the second dammember DM2 is higher than that of a top surface of the first dam memberDM1. The height of each of the first and second dam members DM1 and DM2is defined as a distance from a bottom surface to a top surface of eachof the first and second dam members DM1 and DM2. A space between thefirst dam member DM1 and the second dam member DM2 and a space betweenthe first dam member DM1 and the second and third insulating layers INS2and INS3 are grooves.

According to an embodiment, the first dam member DM1 includes a firstinsulating dam layer DM1_1 disposed on the substrate SUB, a secondinsulating dam layer DM1_2 disposed on the first insulating dam layerDM1_1, and a third insulating dam layer DM1_3 disposed on the secondinsulating dam layer DM1_2. The second dam member DM2 includes a fourthinsulating dam layer DM2_1 disposed on the substrate SUB, a fifthinsulating dam layer DM2_2 disposed on the fourth insulating dam layerDM2_1, a sixth insulating dam layer DM2_3 disposed on the fifthinsulating dam layer DM2_2, and a seventh insulating dam layer DM2_4disposed on the sixth insulating dam layer DM2_3.

According to an embodiment, each of the first to seventh insulating damlayers DM1_1-DM2_4 is formed of or includes an organic material. Thefourth insulating dam layer DM2_1 and the second insulating layer INS2are simultaneously formed of the same material. The first and fifthinsulating dam layers DM1_1 and DM2_2 and the third insulating layerINS3 are simultaneously formed of the same material. The second andsixth insulating dam layers DM1_2 and DM2_3 and the pixel definitionlayer PDL are simultaneously formed of the same material. The third andseventh insulating dam layers DM1_3 and DM2_4 are simultaneously formedof different organic materials.

According to an embodiment, the first encapsulation layer EN1 isdisposed on the substrate SUB and covers the pixels PX of the displayregion DA and the second electrode E2, and the first and second dammembers DM1 and DM2 of the non-display region NDA. The firstencapsulation layer EN1 is spaced back from an edge of the substrate SUBby a predetermined distance.

According to an embodiment, the second encapsulation layer EN2 isdisposed on the first encapsulation layer EN1. The second encapsulationlayer EN2 is disposed in a region defined by the first dam member DM1adjacent to the display region DA. For example, the second encapsulationlayer EN2 is disposed on a region that extends from the display regionDA to a side surface of the first dam member DM1 that faces the displayregion DA.

According to an embodiment, the first encapsulation layer EN1 and thesecond encapsulation layer EN2 include inorganic materials that differfrom each other. For example, the first encapsulation layer EN1 includesa first inorganic material, and the second encapsulation layer EN2includes a second inorganic material that differs from the firstinorganic material. The first and second encapsulation layers EN1 andEN2 can prevent external oxygen and moisture from infiltrating into thepixels.

According to an embodiment, the first inorganic material is siliconoxynitride (SiON). The second inorganic material is silicon oxynitride(SiON) or silicon oxide (SiOx). When both of the first and secondinorganic materials include silicon oxynitride, they differ from eachother in terms of the composition ratios of silicon. (Si), oxygen (O),and nitrogen (N). In this case, the first and second inorganic materialshave refractive indices that differ from each other.

According to an embodiment, a surface roughness of the top surface ofthe second encapsulation layer EN2 is greater than a surface roughnessof the top surface of the first encapsulation layer EN1. Hereinafter,the surface roughness of the top surface of the first encapsulationlayer EN1 will be referred to as a ‘first surface roughness’, and thesurface roughness of the top surface of the second encapsulation layerEN2 will be referred to as a ‘second surface roughness’. The surfaceroughness is a root mean square (RMS) of the vertical height of surfacepoints from a mean line and has units of length, and is a measure ofroughness caused by uneven structures on a surface. The second surfaceroughness is greater than the first surface roughness. For example, thesecond surface roughness ranges from about 8.4 nm to about 35 nm, andthe first surface roughness ranges from about 0.9 nm to about 2 nm.

According to an embodiment, various methods can be used to create thesecond surface roughness that ranges from about 8.4 nm to about 35 nm.For example, to form an inorganic insulating layer, particles made of aninorganic material are randomly provided on the substrate SUB. If anamount of an inorganic material is increased, the inorganic insulatinglayer will have a flat top surface, and if an amount of the inorganicmaterial is decreased, the inorganic insulating layer will have a roughtop surface. Thus, a thinner inorganic insulating layer will have anincreased surface roughness.

According to an embodiment, when the second encapsulation layer EN2 isformed, particles used to form the second encapsulation layer EN2 andformed of a second inorganic material are deposited on the firstencapsulation layer EN1. The amount of the second inorganic material tobe deposited onto the first encapsulation layer is adjusted to controlthe thickness of the second encapsulation layer EN2. The thickness ofthe second encapsulation layer EN2 is controlled so that the secondsurface roughness is greater than the first surface roughness.

According to an embodiment, for the second surface roughness to begreater than the first surface roughness, the thickness of the secondencapsulation layer EN2 is less than that of the first encapsulationlayer EN1. For example, the thickness of the second encapsulation layerEN2 ranges from about 200 Å to about 500 Å.

According to an embodiment, the inorganic insulating layer is depositedby a chemical vapor deposition method. NH₃ gas is used to form aninorganic insulating layer, such as silicon oxynitride (SiON). Here, thelower is the flow rate of the NH₃ gas, the larger is the surfaceroughness of the inorganic insulating layer. In other words, the lowerthe ratio of N to SiON, the larger the surface roughness, i.e., theratio of N to SiON is inversely proportional to the surface roughness.

Thus, according to an embodiment, the second surface roughness iscontrolled by adjusting the flow rate of the NH₃ gas in a process offorming the second encapsulation layer EN2. To enable the second surfaceroughness to be greater than the first surface roughness, the flow rateof the NH₃ gas is reduced when the second encapsulation layer EN2 isformed.

An embodiment of a method of adjusting a thickness and a flow rate ofgas has been described, but embodiments of the inventive concept are notlimited thereto. Various methods of adjusting a power and a gassupplying time can be used to control the second surface roughness.

According to an embodiment, the third encapsulation layer EN3 isdisposed on the second encapsulation layer EN2. The third encapsulationlayer EN3 is formed by curing a fluidic, organic material. The thirdencapsulation layer EN3 planarizes a top surface of the display regionDA.

According to an embodiment, the fourth encapsulation layer EN4 isdisposed on the first encapsulation layer EN1 and covers the thirdencapsulation layer EN3 in the display region DA and a portion of thenon-display region NDA between the display region DA and the first dammember DM1. The fourth encapsulation layer EN4 is formed of or includean inorganic material that differs from the first and secondencapsulation layers EN1 and EN2. For example, the fourth encapsulationlayer EN4 includes silicon nitride (SiNx). The fourth encapsulationlayer EN4 can prevent external oxygen and moisture from infiltratinginto the display panel 110.

According to an embodiment, when the thin encapsulation layer TFE isformed, the fluidic organic material for forming the third encapsulationlayer EN3 is coated on the substrate SUB by an inkjet printing method.If too much organic material is coated, the organic material mayoverflow the substrate SUB because the organic material is fluidic.

In some embodiments, even when too much organic material is coated, theorganic material can be contained in grooves between the first dammember DM1 and the second dam member DM2 and between the first dammember DM1 and the second and third insulating layers INS2 and INS3.This can prevent the organic material from overflowing the substrateSUB.

According to an embodiment, the higher is the surface roughness, thegreater is the spreadability of the fluid. The lower is the surfaceroughness, the lower is the fluid spreadability. The relationshipbetween surface roughness and fluid spreadability will be described inmore detail, when a method of fabricating a display device is described.

According to an embodiment, since the second encapsulation layer EN2 hasa surface roughness greater than that of the first encapsulation layerEN1, a fluidic organic material can more effectively spread on thesecond encapsulation layer EN2 than on the first encapsulation layerEN1. That is, the second encapsulation layer EN2 has a high affinitywith the organic material. By contrast, the organic material does notspread on the first encapsulation layer EN1, which has a lower surfaceroughness than the second encapsulation layer EN2. That is, the firstencapsulation layer EN1 has a low affinity with the organic material.

According to an embodiment, when an organic material for forming thethird encapsulation layer EN3 is disposed on the second encapsulationlayer EN2, the organic material effectively spreads on the secondencapsulation layer EN2 but does not spread on the first encapsulationlayer EN1. Thus, an organic material can be formed on only a desiredregion and be prevented from overflowing the substrate SUB.

As a result, in the display device 100 according to some embodiments ofthe inventive concept, an organic material for forming the thirdencapsulation layer EN3 can be formed on a desired region and beprevented from overflowing the substrate SUB.

FIGS. 6 to 11 are sectional views that illustrate a method offabricating a display device according to some embodiments of theinventive concept.

For convenience of illustration, a left portion of the sectional view ofFIG. 4 is illustrated in FIGS. 6, 7, 8, and 11.

Referring to FIG. 6, according to an embodiment, the substrate SUB thatincludes the display region DA and the non-display region NDA isprepared. The pixels PX are disposed on the display region DA, and thefirst and second dam members DM1 and DM2 are disposed on the non-displayregion NDA.

According to an embodiment, the first encapsulation layer EN1 isdisposed on the substrate SUB that cover the pixels PX and the first andsecond dam members DM1 and DM2. In some embodiments, a first mask M1that has a first opening OP1 is provided on the first insulating layerINS1 in an edge region of the substrate SUB. The first opening OP1exposes a region from the display region DA past second dam member DM2up to a predetermined distance from the edge of the substrate SUB.

According to an embodiment, a first inorganic material IOR1 is suppliedonto the substrate SUB through the first opening OP1. In someembodiments, the first inorganic material IOR1 is used to cover thepixels PX, the second electrode E2, and the first and second dam membersDM1 and DM2 and to form the first encapsulation layer EN1 on thesubstrate SUB. Since the first encapsulation layer EN1 is formed usingthe first opening OP1 of the first mask M1, the first encapsulationlayer EN1 is spaced apart from the edge of the substrate SUB by thepredetermined distance.

Referring to FIG. 7, according to an embodiment, a second mask M2 thathas a second opening OP2 is provided on the substrate SUB, and here, thesecond opening OP2 exposes the display region DA and a portion, such asa side surface, of the first dam member DM1. When a mask is positionedclose to a substrate, it is possible to more precisely deposit adeposition material on a desired region. In this case, the second maskM2 is placed adjacent to a top surface of the second dam member DM2. Forexample, in some embodiments, the second mask M2 is in contact with thetop surface of the first encapsulation layer EN1 on the second dammember DM2.

According to an embodiment, a second inorganic material IOR2 is suppliedonto the first encapsulation layer EN1 through the second opening OP2 toform the second encapsulation layer EN2. Due to the afore-describedshape of the second opening OP2, the second inorganic material IOR2 issupplied to a region that extends from the display region DA to the sidesurface of the first dam member DM1. Thus, the second encapstilationlayer EN2 is formed on the first encapsulation layer EN1 and covers theregion from the display region DA to the side surface of the first dammember DM1.

As described above, according to an embodiment, the thickness of thesecond encapsulation layer EN2 and the flow rate of gas in thedeposition process of the second inorganic material IOR2 are adjusted toenable the second encapsulation layer EN2 to have a second surfaceroughness that ranges from about 8.4 nm to about 35 nm. In addition, thesecond encapsulation layer EN2 has a thickness less than that of thefirst encapsulation layer EN1.

Referring to FIG. 8, according to an embodiment, an organic material ORis supplied onto the second encapsulation layer EN2 to form the thirdencapsulation layer EN3. In some embodiments, an inkjet printing methodis used to supply the organic material OR onto the second encapsulationlayer EN2 through a nozzle NOZ.

Referring to FIGS. 9 and 10, according to an embodiment, a top surfaceof a first layer LAY1_2 shown in FIG. 10 is formed to have a surfaceroughness greater than that of a top surface of a first layer LAY1_1shown in FIG. 9. Second protruding portions P2 on the top surface of thefirst layer LAY1_2 of FIG. 10 are more densely provided than firstprotruding portions P1 on the top surface of the first layer LAY1_1 ofFIG. 9. For example, a first distance D1 between two adjacent firstprotruding portions P1 is greater than a second distance D2 between twoadjacent second protruding portions P2.

As shown in FIG. 9, according to an embodiment, when a fluid LQ isprovided on the first layer LAY1_1, it takes a long time for the fluidLQ to fill first grooves G1 between the first protruding portions P1.However, as shown in FIG. 10, when the fluid LQ is provided on the firstlayer LAY1_2, it takes a short time for the fluid LQ to fill secondgrooves G2 between the second protruding portions P2. That is, as shownin FIG. 10, the greater the surface roughness, the more easily the fluidLQ can spread.

According to an embodiment, considering the relationship between surfaceroughness and fluid spreadability, which was described with reference toFIGS. 9 and 10, and the structure shown in FIG. 8, the organic materialOR has a high spreadability on the second encapsulation layer EN2 havinga high surface roughness. Thus, the organic material OR can effectivelyspread on the second encapsulation layer EN2, but will not effectivelyspread on the first encapsulation layer EN1.

According to an embodiment, the organic material OR is contained in thegrooves between the first dam member DM1 and the second and thirdinsulating layers INS2 and INS3, and thus, the organic material OR doesnot spread to a region of the first encapsulation layer EN1 beyond anedge of the second encapsulation layer EN2. Accordingly, the organicmaterial OR can be formed only on a desired region and be moreeffectively prevented from overflowing the substrate SUB.

Referring to FIG. 11, according to an embodiment, the fourthencapsulation layer EN4 is formed on the first encapsulation layer EN1and covers the third encapsulation layer EN3, and as a result, thedisplay device 100 is fabricated.

FIGS. 12 and 13 are sectional views that illustrate a method offabricating a display device according to other embodiments of theinventive concept.

In a present embodiment, a single mask is used to form first and secondencapsulation layers EN1 and EN2. Except for this, a fabrication methodof FIGS. 12 and 13 can be performed in the same manner as in FIGS. 6 to11. In the following description of FIGS. 12 and 13, an element or steppreviously described with reference to FIGS. 6 to 11 may be identifiedby the same reference number without repeating description thereof, forthe sake of brevity.

Referring to FIG. 12, according to an embodiment, a process ofdepositing an inorganic material is performed using a mask M in a vacuumchamber and spaced apart from the substrate SUB. The mask M ispositioned near a top surface of the vacuum chamber or is spaced apartfrom the substrate SUB by a predetermined distance.

According to an embodiment, the first inorganic material IOR1 issupplied onto the substrate SUB to form the first encapsulation layerEN1′ and cover the pixels PX, the second electrode E2, and the first andsecond dam members DM1 and DM2. Since the mask M is spaced apart fromthe substrate SUB, the mask M does not block the first inorganicmaterial IOR1. Thus, the first inorganic material IOR1 can be suppliedonto the end portion of the substrate SUB. As a result, the firstencapsulation layer EN1′ covers the entire top surface of the substrateSUB or at least the end portion of the substrate SUB.

Referring to FIG. 13, according to an embodiment, the mask M is providedwith an opening OP. For example, the mask M has substantially the sameshape as the second mask M2. That is, the opening OP of the mask Mexpose a region that extends from the display region DA to the sidesurface of the first dam member DM1. The mask M is positioned adjacentto the top surface of the first dam member DM1, similar to the secondmask M2.

According to an embodiment, the second inorganic material IOR2 issupplied onto the first encapsulation layer EN1′ through the opening OPto form the second encapsulation layer EN2. For example, the secondinorganic material IOR2 covers the region from the display region DA tothe side surface of the first dam member DM1. As a result, the secondencapsulation layer EN2 is formed on the first encapsulation layer EN1′and covers a region from the display region DA to the side surface ofthe first dam member DM1. The third encapsulation layer EN3 and thefourth encapsulation layer EN4 are formed on the substrate SUB by thesame method as that described with reference to FIGS. 8 and 11, and adetailed description thereof will be omitted.

According to some embodiments of the inventive concept, a method offabricating a display device include forming a second encapsulationlayer whose affinity with an organic material is high on a firstencapsulation layer and then forming an organic material on the secondencapsulation layer to form a third encapsulation layer. Accordingly,the organic material for the third encapsulation layer can be placed ina desired region and be prevented from overflowing a substrate.

While exemplary embodiments of the inventive concept have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

What is claimed is:
 1. A display device, comprising: a substrate thatincludes a display region and a non-display region that surrounds thedisplay region; a plurality of pixels disposed on the display region ofthe substrate; a plurality of dam members disposed on the non-displayregion of the substrate that surround the display region; a firstencapsulation layer disposed on the substrate that covers the pluralityof pixels and the plurality of dam members; a second encapsulation layerdisposed on the first encapsulation layer and in a region between thedisplay region and a dam member of the plurality of dam members that isadjacent to the display region; a third encapsulation layer provided onthe second encapsulation layer, and a fourth encapsulation layerdisposed on the first encapsulation layer that covers the thirdencapsulation layer, wherein a surface roughness of a top surface of thesecond encapsulation layer is greater than a surface roughness of a topsurface of the first encapsulation layer.
 2. The display device of claim1, wherein a thickness of the second encapsulation layer is less than athickness of the first encapsulation layer.
 3. The display device ofclaim 1, wherein the surface roughness of the second encapsulation layerranges from 8.4 nm to 35 nm, and the surface roughness of the firstencapsulation layer ranges from 0.9 nm to 2 nm.
 4. The display device ofclaim 1, wherein the first encapsulation layer comprises a firstinorganic material, and the second encapsulation layer comprises asecond inorganic material that differs from the first inorganicmaterial.
 5. The display device of claim 4, wherein the first inorganicmaterial is silicon oxynitride, the second inorganic material is siliconoxynitride or silicon oxide, and the first and second inorganicmaterials differ from each other in terms of composition ratios ofsilicon, oxygen, and nitrogen.
 6. The displays device of claim 1,wherein the plurality of dam members comprise: a first dam member thatsurrounds the display region; and a second dam member that surrounds thefirst dam member, wherein a height of a top surface of the second dammember is higher than that of a top surface of the first dam member. 7.The display device of claim 6, wherein the second encapsulation layercovers a region from the display region to a side surface of the firstdam member that faces the display region.
 8. The display device of claim6, wherein the first dam member comprises: a first insulating dam layerdisposed on the substrate; a second insulating dam layer disposed on thefirst insulating dam layer; and a third insulating dam layer disposed onthe second insulating dam layer.
 9. The display device of claim 8,wherein the second dam member comprises: a fourth insulating dam layerdisposed on the substrate; a fifth insulating dam layer disposed on thefourth insulating dam layer; a sixth insulating dam layer disposed onthe fifth insulating dam layer; and a seventh insulating dam layerdisposed on the sixth insulating dam layer.
 10. The display device ofclaim 9, wherein each of the first to seventh insulating dam layerscomprises an organic material.
 11. The display device of claim 1,wherein the third encapsulation layer comprises an organic material, andthe fourth encapsulation layer comprises an inorganic material differentfrom those of the first and second encapsulation layers.
 12. A displaydevice, comprising: a substrate that includes a display region and anon-display region that surrounds the display region; a plurality ofpixels disposed on the display region of the substrate; a plurality ofdam members disposed on the non-display region of the substrate thatsurround the display region; a first encapsulation layer disposed on thesubstrate that covers the plurality of pixels and the plurality of dammembers; a second encapsulation layer disposed on the firstencapsulation layer and in a region between the display region and a dammember of the plurality of dam members that is adjacent to the displayregion; a third encapsulation layer provided on the second encapsulationlayer; and a fourth encapsulation layer disposed on the firstencapsulation layer that covers the third encapsulation layer, whereinthe first encapsulation layer comprises silicon oxynitride, the secondencapsulation layer comprises silicon oxynitride or silicon oxide, andthe first and second inorganic materials differ from each other in termsof composition ratios of silicon, oxygen, and nitrogen.
 13. The displaydevice of claim 12, wherein a surface roughness of a top surface of thesecond encapsulation layer is greater than a surface roughness of a topsurface of the first encapsulation layer, and a thickness of the secondencapsulation layer is less than a thickness of the first encapsulationlayer.
 14. A method of fabricating a display device, comprising:preparing a substrate that includes a display region and a non-displayregion that surrounds the display region; forming a plurality of pixelson the display region of the substrate; forming a plurality of dammembers on the non-display region of the substrate that surround thedisplay region; forming a first encapsulation layer on the substratethat covers the pixels and the dam members; and forming a secondencapsulation layer on the first encapsulation layer and in a regionbetween the display region and a dam member of the plurality of dammembers that is adjacent to the display region; forming a thirdencapsulation layer on the second encapsulation layer; and forming afourth encapsulation lager on the first encapsulation layer to cover thesecond encapsulation and the third encapsulation layer, wherein thesecond encapsulation layer has a top surface whose surface roughness isgreater than a surface roughness of a top surface of the firstencapsulation layer.
 15. The method of claim 14, wherein the pluralityof dam members comprise: a first dam member that surrounds the displayregion; and a second dam member that surrounds the first dam member,wherein a height of a top surface of the second dam member is higherthan that of a top surface of the first dam member, and the secondencapsulation layer covers a region from the display region to a sidesurface of the first dam member that faces the display region.
 16. Themethod of claim 15, wherein forming the first encapsulation layercomprises: providing a first mask on the substrate that has a firstopening that exposes the display region and the first and second dammembers; and supplying a first inorganic material onto the substratethrough the first opening to cover the pixels and the first and seconddam members and from the first encapsulation layer.
 17. The method ofclaim 16, wherein forming the second encapsulation layer comprises:providing a second mask on the substrate that has a second opening thatexposing a region that extends from the display region to the sidesurface of the first dam member that faces the display region; andsupplying a second inorganic material onto the first encapsulation layerthrough the second opening to cover a region from the display region tothe side surface of the first dam member that faces the display regionand form the second encapsulation layer, wherein the second mask ispositioned adjacent to a top surface of the first dam member, whereinthe second inorganic material is different from the first inorganicmaterial, and wherein the third encapsulation layer comprises an organicmaterial.
 18. The method of claim 17, wherein a thickness of the secondencapsulation layer and a flow rate of NH₃ gas used in supplying thesecond inorganic material are adjusted to enable the surface roughnessof the second encapsulation layer to be greater than the surfaceroughness of the first encapsulation layer.
 19. The method of claim 15,wherein forming the first encapsulation layer comprises supplying afirst inorganic material onto the substrate to cover the pixels and thefirst and second dam members and form the first encapsulation layer,forming the second encapsulation layer comprises: providing a mask onthe substrate, the mask having an opening exposing a region from thedisplay region to the side surface of the first dam member that facesthe display region; and supplying a second inorganic material onto thefirst encapsulation layer through the opening to cover the region fromthe display region to the side surface of the first dam member thatfaces the display region to form the second encapsulation layer, and themask is positioned adjacent to a top surface of the first dam member.